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Home / Equine Research Bank / Vet J / Atrial fibrillation in horses part 1: Pathophysiology.
Veterinary journal (London, England : 1997)2020; 263; 105521; doi: 10.1016/j.tvjl.2020.105521

Atrial fibrillation in horses part 1: Pathophysiology.

Abstract: Atrial fibrillation (AF) is the most common clinically relevant arrhythmia in horses, with a reported prevalence up to 2.5%. The pathophysiology has mainly been investigated in experimental animal models and human medicine, with limited studies in horses. Atrial fibrillation results from the interplay between electrical triggers and a susceptible substrate. Triggers consist of atrial premature depolarizations due to altered automaticity or triggered activity, or local (micro)reentry. The arrhythmia is promoted by atrial myocardial ion channel alterations, Ca2+ handling alterations, structural abnormalities, and autonomic nervous system imbalance. Predisposing factors include structural heart disease such as valvular regurgitation resulting in chronic atrial stretch, although many horses show so-called 'lone AF' or idiopathic AF in which no underlying cardiac abnormalities can be detected using routine diagnostic techniques. These horses may have underlying ion channel dysfunction or undiagnosed myocardial (micro)structural alterations. Atrial fibrillation itself results in electrical, contractile and structural remodelling, fostering AF maintenance. Electrical remodelling leads to shortening of the atrial effective refractory period, promoting reentry. Contractile remodelling consists of decreased myocardial contractility, while structural remodelling includes the development of interstitial fibrosis and atrial enlargement. Reverse remodelling occurs after cardioversion to sinus rhythm, but full recovery may take weeks to months depending on duration of AF. The clinical signs of AF depend on the aerobic demands during exercise, ventricular rhythm response and presence of underlying cardiac disease. In horses with so-called 'lone AF', clinical signs are usually absent at rest but during exercise poor performance, exercise-induced pulmonary hemorrhage, respiratory distress, weakness or rarely collapse may develop.
Copyright © 2020 Elsevier Ltd. All rights reserved.
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Publication Date: 2020-07-23 PubMed ID: 32928494DOI: 10.1016/j.tvjl.2020.105521Google Scholar: Lookup
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Summary

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This research article reviews the pathophysiology of atrial fibrillation (AF), the most common clinical cardiac irregularity observed in horses. The research also investigates certain predisposing factors and alterations that could instigate AF, such as structural heart disease, and gives further insight into how the condition evolves and influences the cardiac function of a horse.

Understanding Atrial Fibrillation

  • Atrial fibrillation is a heart disorder affecting the atrium’s rhythm. It is the most recurrent clinical arrhythmia seen in horses, with rates reaching as high as 2.5%.
  • This condition stems from a combination of electrical triggers and an exposed substrate. These triggers can take the form of premature depolarizations in the atria due to changes in automaticity or triggered activity, or localized microreentry.
  • The progression of the disorder is influenced by alterations in atrial myocardial ion channels, Ca handling mechanisms, structural anomalies, and imbalances in the autonomic nervous system.

Underlying Predisposing Factors

  • Structural heart disease is one of the major predisposing factors leading to AF. Conditions like valvular regurgitation result in persistent atrial stretch which can instigate AF.
  • ‘Lone AF’ or idiopathic AF is a form of the disorder where no clear underlying cardiac issue is detected using standard diagnostic procedures. Horses with this condition may suffer from undiagnosed microstructural alterations in the heart’s muscle or ion channel dysfunctions.

Atrial Fibrillation Remodelling Impact

  • The occurrence of atrial fibrillation leads to electrical, contractile, and structural remodelling. This remodelling process furthers the maintenance of AF within the heart.
  • Electrical remodelling results in a shortening of the atrial effective refractory period, promoting reentry. Contractile remodelling reduces myocardial contractility, while structural remodelling leads to interstitial fibrosis and atrial enlargement.
  • Reverse remodelling occurs post cardioversion to sinus rhythm, but complete recovery could take weeks or even months depending on the duration of AF.

Clinical Symptoms of Atrial Fibrillation

  • The clinical signs associated with atrial fibrillation are contingent on the aerobic demands during exercise, the ventricular rhythm response, and the presence of underlying cardiac anomalies.
  • Horses with ‘lone AF’ generally don’t exhibit clinical symptoms at rest. However, during exercise, they may display poor performance, exercise-induced pulmonary hemorrhage, respiratory distress, weakness or in rare cases, may collapse.

Cite This Article

APA
Decloedt A, Van Steenkiste G, Vera L, Buhl R, van Loon G. (2020). Atrial fibrillation in horses part 1: Pathophysiology. Vet J, 263, 105521. https://doi.org/10.1016/j.tvjl.2020.105521

Publication

Veterinary journal (London, England : 1997)
ISSN: 1532-2971
NlmUniqueID: 9706281
Country: England
Language: English
Volume: 263
Pages: 105521

Researcher Affiliations

Decloedt, Annelies
  • Equine Cardioteam Gent University, Department of Large Animal Internal Medicine, Faculty of Veterinary Medicine, Ghent University, Belgium. Electronic address: annelies.decloedt@ugent.be.
Van Steenkiste, Glenn
  • Equine Cardioteam Gent University, Department of Large Animal Internal Medicine, Faculty of Veterinary Medicine, Ghent University, Belgium.
Vera, Lisse
  • Equine Cardioteam Gent University, Department of Large Animal Internal Medicine, Faculty of Veterinary Medicine, Ghent University, Belgium.
Buhl, Rikke
  • Department of Veterinary Clinical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark.
van Loon, Gunther
  • Equine Cardioteam Gent University, Department of Large Animal Internal Medicine, Faculty of Veterinary Medicine, Ghent University, Belgium.

MeSH Terms

  • Animals
  • Atrial Fibrillation / etiology
  • Atrial Fibrillation / physiopathology
  • Atrial Fibrillation / veterinary
  • Atrial Remodeling / physiology
  • Autonomic Nervous System / physiopathology
  • Calcium / metabolism
  • Electrophysiological Phenomena
  • Heart / physiopathology
  • Heart Atria / pathology
  • Heart Atria / physiopathology
  • Heart Valve Diseases / complications
  • Heart Valve Diseases / veterinary
  • Horse Diseases / diagnosis
  • Horse Diseases / etiology
  • Horse Diseases / physiopathology
  • Horses
  • Ion Channels / physiology
  • Myocardium / chemistry
  • Myocardium / pathology

Citations

This article has been cited 15 times.
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